Printers are imaging devices that print onto a printing medium such as a sheet of paper or a polyester film. Printers of many types are available and are commonly controlled by a computer that supplies the images in the form of text or figures that are to be printed. One type of imaging device is the ink jet printer, which forms small droplets of ink that are ejected toward the printing medium in a pattern of dots or pixels that form the images.
An ink jet printer typically has a large number of individual colorant-ejection nozzles in a printhead. A printhead is supported in a carriage and oriented in a facing, but spaced-apart, relationship to the printing medium. The carriage and supported printhead traverse over the surface of the medium with the nozzles ejecting droplets of colorant at appropriate times under command of the computer or other controller to produce a swath of ink droplets.
The printhead typically uses water as the vehicle or solvent to carry the ink or colorant droplets. The droplets strike the medium to form dots that when viewed together form one swath or row of the printed image. The carriage is moved an increment in the direction lateral to traverse (or, alternatively, the printing medium is advanced), and the carriage again traverses the page with the printhead operating to deposit another swath. In this manner, the entire pattern of dots that form the image is progressively deposited by the printhead during a number of traverses of the page.
Good print quality is one of the most important considerations and basis of competition in the ink jet printer industry. Since an ink jet printer forms images with individual dots, the quality of the image is ultimately dependent upon the quality of each dot and the arrangement of the dots on the print medium. Because of the fashion in which printing occurs, the quality of the dots can have a surprisingly large effect upon the final image quality. Thus, there has existed a need to make dots or images smear-proof or water-fast, and resistant to physical abrasion.
One traditional technique to reduce ink jet image smearing and increase image abrasion resistance includes laminating a clear film over the top of a printed image after the image has been rendered onto an ink receiver. This traditional technique, however, is substantially problematic for a number of reasons. For instance, the lamination process is typically time-consuming and often produces unusable prints or waste due to print handling and/or air bubbles trapped between the laminate and the printed image. Additionally, this conventional technique to reduce ink jet image smearing and increase image abrasion resistance generally increases overall printing and equipment costs due to the extra image lamination sheets and laminating apparatus required.
Another conventional technique to reduce ink jet image smearing and increase image abrasion resistance requires the deposit of a chemical precursor (e.g., a cross-linkable gelatin mixture) on the ink recording medium before depositing the ink on the print medium. This chemical precursor preconditions the print medium to react with other functional chemicals such as aldehydes, acid chlorides, and/or double bond chemicals. These functional chemicals are generally either mixed directly with the ink, or mixed together in a pen separate from the ink pens, and sprayed over the ink to reduce ink drying time, paper cockle, and/or color bleed. Such preconditioning is typically time consuming and very expensive.
Moreover, mixing such functional chemicals with one another in a single pen that is separate from the ink or in combination with the ink is substantially problematic. One problem, for instance, is that such functional chemicals are typically extremely reactive and may react with one another in a hazardous manner—resenting flammability and toxicity issues as well as other health risks both before and after they have even been deposited onto the chemical precursor on the ink receiver. Such hazardous reactions generally require that consumers be appropriately forewarned with visible warning labels.
Additionally, mixing levels of protective polymers that are needed to provide reasonable protective film formation over an image in the same printhead that is used to deposit the ink will typically reduce the reliability of the printhead. This is because mixing a protective polymer with the ink substantially increases the mixture's viscosity. This increased viscosity generally results in undesirable printhead nozzle clogging and thereby reduces printhead reliability. Attempting to avoid such printhead nozzle clogs, conventional systems add only a limited amount of the functional polymer. Unfortunately, this limited amount is typically less than the levels of protective polymers that are needed to provide reasonable reliability or proper protective film formation over an image.
The following described arrangements and procedures address these and other problems with protecting images formed on a print media substrate.